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is gradually added to the warm solution.*1 The cuprous cyanide
dissolves in excess of the potassium cyanide and cyanogen g'as
is liberated. 2CuSO4 + 4KCN = 2CuCN + 2K2S04 + (CN)2-
The solution is left, whilst the /-toluidine is diazotised.
The base is dissolved in the dilute hydrochloric acid, cooled, in
ice, and well stirred. The mixture is kept cold whilst the sodium
nitrite solution is gradually added, until it gives an immediate
colouration with potassium iodide-starch paper. The clia-zo-
solution is then added in portions of about 10 c.c. at a
time to the warm cuprous cyanide solution, with frequent
shaking. A rapid effervescence occurs, nitrogen and some
hydrocyanic acid being evolved. When, in the course of a/bout
fifteen minutes, the diazo-solution has been added, it is left
on the water-bath until effervescence ceases (J hour). The
liquid turns a dark colour, and a black tarry deposit is
formed. The product is distilled in steam. This should be
carried out in the fume cupboard, as not only is hydrocyanic
acid liberated, but a small quantity of isocyanide, which is formed
inthe reaction, and produces an intolerable smell. The distillation
is continued until no more yellow oil passes over. The tolyl
cyanide solidifies in the receiver on cooling as a yellow crystal-
line mass, which is filtered, dried on a porous plate, and may be
purified by distillation ; but for the preparation of toluic acid
this is unnecessary. Yield about 15 grams.

CH3.C0H4NHo.HCl + NaN02+ HC1 = CH3.CflH4N2CHh

Properties. Colourless crystals ; m. p. 29 ; b. p. 218.

Reaction.  p-Toluic Acid.  Boil up 10 grams tolylcyanide
with a mixture of 30 c.c. cone, sulphuric acid and 20 c.c. water, in a.
round flask with upright condenser until colourless crystals of
toluic acid appear in the condenser tube (about half an hour). On
cooling, the acid crystallises out, and is separated by filtration,
washed with water, and recrystallised from hot water ; m. p. I 79.

CH3.CGH4.CN + 2HoO -1- H9S04 = CH3.C6H4.CO.OM
+ NH4.H.SOi.

if    |                       The yield is nearly theoretical.